2.1. Citrus Limonoids
Limonoids are a group of chemically related triterpene derivatives found in the Rutaceae and Meliaceae families. Limonoids are among the bitter principles found in citrus fruits such as lemons, lime, orange and grapefruit. They are also present as glucose derivatives in mature fruit tissues and seed, and are one of the major secondary metabolites present in Citrus. Limonoids have been found to have anti-carcinogenic activity in laboratory animals. The furan moiety attached to the D-ring is specifically responsible for detoxifying of the chemical carcinogen by induction of the liver glutathione-S-transferase enzyme system (Lam, et al., 1994, Food Technol. 48:104-108).
Citrus fruit tissues and by-products of juice processing such as peels and molasses are sources of limonoid glucosides and citrus seeds contain high concentrations of both limonoid aglycones and glucosides. Limonoid agylycones in the fruit tissues gradually disappear during the late stages of fruit growth and maturation.
Thirty-eight limonoid aglycones have been isolated from Citrus. The limonoids are present in three different forms: the dilactone (I) is present as the open D-ring form (monolactone), the limonoate A-ring lactone (II) and the glucoside form (III). Only the monolactones and glucosides are present in fruit tissues. (Hasegawa S. et al., 1994, in Food Phytochemicals for Cancer Prevention I, eds M-T. Huang et al., American Chemical Society, 198-207). ##STR1##
Compound III is the predominant limonoid glucoside found in all juice samples. In orange juice it comprises 56% of the total limonoid glucosides present, while in grapefruit and lemon juices, it comprises an average of 63% to 66% respectively. Procedures for the extraction and isolation of both aglycones and glucosides have been established to obtain concentrated sources of various limonoids (Lam, L. K. T. et al., 1994, in Food Phytochemicals for Cancer Prevention, eds. M. Huang, T. Osawa, C. Ho and R. T. Rosen, ACS Symposium Series 546, p 209). The use of limonoids alone or in combination with a citrus flavonoid, tocotrienol, a cancer chemotherapeutic agent, or a combination of any one of these agents, has not been reported for the prevention and treatment of neoplastic diseases.
2.2. Citrus Flavonoids
Epidemiological studies have shown that flavonoids present in the Mediterranean diet may reduce the risk of death from coronary heart disease (Hertog, M. G. et al., 1993, Lancet: 342, 1007-1011). Soybean isoflavones for example, genistein, which is a minor component of soy protein preparations may have cholesterol-lowering effects (Kurowska, E. M. et al., 1990, J. Nutr. 120:831-836). The flavonoids present in citrus juices such as orange and grapefruit include, but are not limited to, hesperetin and naringenin respectively. The use of flavonoids from citrus juices alone or in combination with a citrus limonoid, tocotrienol, a cholesterol--lowering drug, or a combination of any one of these agents, has not been reported for the treatment of hypercholesterolemia.
##STR2## 5 7 3' 4' HESPERETIN OH OH OH OCH.sub.3 NARINGENIN OH OH -- OH
The flavonoids preset in tangerine include, but are not limited to tangeretin or nobiletin. These flavonoids were found to inhibit growth of both estrogen receptor-negative (ER-) and positive (ER+) breast cancer cells in culture and act synergistically with tamoxifen and tocotrienols (Guthrie N. et al., 1996, Proc. Am. Inst. Cancer Res., Abs. #8).
 ##STR3## 5 6 7 8 4' 5' TANGERETIN OCH.sub.3 OCH.sub.3 OCH.sub.3 OCH.sub.3 OCH.sub.3 -- NOBILETIN OCH.sub.3 OCH.sub.3 OCH.sub.3 OCH.sub.3 OCH.sub.3 OCH.sub.3
2.3 Tocotrienols in Palm Oil
Tocotrienols are present in palm oil and are a form of vitamin E having an unsaturated side chain. They include, but are not limited to alpha-tocotrienol, gamma-tocotrienol or delta-tocotrienol.
 ##STR4## R1 R2 R3 .alpha.-tocotrienol CH.sub.3 CH.sub.3 CH.sub.3 .gamma.-tocotrienol H CH.sub.3 CH.sub.3 .delta.-tocotrienol H H CH.sub.3
2.4. Cancer Growth and Chemotherapy
Cancer is a disease of inappropriate tissue accumulation. Chemotherapeutic agents share one characteristic: they are usually more effective in killing or damaging malignant cells than normal cells. However, the fact that they do harm normal cells indicates their potential for toxicity. Animal tumor investigations and human clinical trials have shown that drug combinations produce higher rates of objective response and longer survival than single agents. Combination drug therapy is, therefore, the basis for most chemotherapy employed at present (DeVita, V. T. et.al., 1995, Cancer 35:98).
Cancer treatment requires inhibitions of a variety of factors including tumor cell proliferation, metastatic dissemination of cancer cells to other parts of the body, invasion, tumor-induced neovascularization, and enhancement of host immunological responses and cytotoxicity. Conventional cancer chemotherapeutic agents have often been selected on the basis of their cytotoxicity to tumor cells. However, some anticancer agents have adverse effects on the patient's immune system. Thus it would be greatly advantageous if a cancer therapy or treatment could be developed that would afford non-cytotoxic protection against factors that might lead to progression of tumors.
Because hormone therapy as well as chemotherapy is effective in controlling advanced breast cancer, it has been used as an adjuvant to mastectomy in primary breast cancer. Patients with ER+ or ER- tumors benefit from adjuvant chemotherapy. However, tamoxifen used alone as an adjuvant to mastectomy for breast cancer shows benefit in extending disease-free and overall survival (Cummings, F. J. et al., 1985, Ann. Intern. Med. 103;324).